ANGULAR EXPANSION IN PLANETARY NEBULAE FROM RADIO INTERFEROMETRIC DATA

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ANGULAR EXPANSION IN PLANETARY NEBULAE FROM RADIO
INTERFEROMETRIC DATA

• Yolanda Gómez

Centro de Radioastronomía y Astrofísica, UNAM
México
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Colaborators

• Lizette Guzmán (CRyA, UNAM, México)
• Luis F. Rodríguez (CRyA, UNAM, México)

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Angular expansion technique

• A geometrical method in which we substract two
  images, taken over a period of a few years, to
  estimate the angular expansion rate of the
  nebula,
• First applied by Masson (1986) to radio
  interferometric data to estimate distances to
  PNe.

v
Dv/
D
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Some examples
(Masson 1986 1989)
NGC 7027

• This technique has been applied with success
  to several PNe e.g. NGC6302 (Gómez et al. 1993)
  , NGC6572 (Hajian et al. 1995) , Vy 2-2
  (Christianto Seaquist 1998).
• For PNe with distances gt 1 kpc the expected
  angular expansion rate is lt 2 mas/yr.

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Planetary Nebula M 2-43
(Guzmán, Gómez Rodríguez 2006)
1999.721995.65
1999.721995.65
VLA 3.6 cm

• This is the largest distance for a PN
  measured, up to now, with the angular expansion
  technique.

See poster by Guzmán et al.
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Other application for the angular expansion
technique
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The Saturn Nebula NGC 7009

• The ansae (handles) are present in PNe with
  bipolar, rotating, episodic jets ( BRETS e.g.
  López et al. 1995) and fast, low ionization
  emission regions (FLIERS Balick et al. 1993).
• In NGC 7009 the ansae are moving at about 100
  km/s in the plane of the sky, relative to the
  nucleus (Reay Atheton 1985 Balick et al.
  1987).
• The ansae are possibly the termination points of
  the jets (Balick et al. 1987 López et al. 2000
  Steffen et al. 2001).

ansae
HST
Red NII green OIII blue He II
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Proper motions of ansae
Optical

• Few measurements of proper motions of ansae
  KjPn 8 (Meaburn 1997), Hen 2-90 (Sahai et al.
  2002), NGC7009 (Fernández et al. 2004).
• NGC 7009 From
  photographic plates a PM of 16 3 mas/yr
  (Liller 1965)
• From HST images a PM for the eastern ansa of 28
  8 mas/yr (Fernández et al. 2004) is derived.

NGC 7009
HST images of the east ansa (Fernández, Monteiro
Schwarz 2004)
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Applying the angular expansion technique to NGC
7009 to measure proper motions of the ansae at
radio.
VLA
Observations
VLA 3.6 cm

• Archive VLA data for NGC 7009 at 3.6 cm in two
  epochs 1989.24 and 1997.33

NGC 7009
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Ansae proper motions
23 /- 6 mas/yr
Eastern
34 /- 10 mas/yr
(Rodríguez Gómez 2007, RevMexAA, 43, 173)
Western
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Derived parameters for the ansae NGC 7009

• Assuming D 860 /- 340 pc, the velocities of the
  ansae in the plane of the sky are
• EAST ansa 100 /- 50 km/s
• WEST ansa 140 /- 70 km/s
• If the ansae are moving ballistically the
  estimated age is
• 300 years if they originated from the main
  body
• 850 years if they originated from the
  central star.

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Upper limit to the expansion

• The flux density of the main body remains
  constant.
• The flux density of the jets decreased in 30.
  With an electron density 1000 4000 cm-3
  (Bohigas et al. 1994 Goncalves et al. 2003) the
  recombination timescales are between 30 to 120
  yrs.

D 700 pc
Lower limit consistent with the average of 14
available values (Acker et al. 1992 Fernández et
al. 2004), 860 /- 340 pc.
Difference image
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Conclusions

• Interferometric data taken with a few years of
  separation can reveal the angular expansion of
  the nebula and it is possible to estimate its
  distance (e.g. M 2-43 Guzmán et al. 2006).
• This is the first time that proper motions of
  ansae in PNe are determined with radio
  observations (NGC 7009 Rodríguez Gómez 2007).

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Thank you